Population Ecology

Ch. 9

Population Ecology Outline

• • • •

9-1: Population Dynamics and Carrying Capacity 9-2: Reproductive Patterns and Survival 9-3: Effects of Genetic Variations n Pop. Size 9-4: Human Impacts and Working with Nature

9-1: Population Dynamics and Carrying Capacity

•

Population

- individuals of the same species, inhabiting the same area at the same time.

•

Population Dynamics:

Population change due to –

Population Size

- number of individuals –

Population Density

- population size in a certain space at a given time –

Population Dispersion

- spatial pattern in habitat –

Age Structure

- proportion of individuals in each age group in population

Population Density

•

Population Density

(or ecological population density)

is the amount of individuals in a population per unit habitat area – Some species exist in high densities -

Mice

– Some species exist in low densities -

Mountain lions

•

Density depends upon:

– social/population structure – mating relationships – time of year

Population Dispersion

Population dispersion

is the spatial pattern of distribution.

There are 3 main patterns of dispersion:

1. Clumped

: individuals are lumped into groups

ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions; most common

http://www.johndarm.clara.net/galleryphots/

Population Dispersion

2) Uniform:

Individuals are regularly spaced in the environment -

ex. Creosote bush due to antagonism between individuals.

3) Random:

Individuals are randomly dispersed in the environment

ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met

http://www.calflora.net/bloomingplants/creosotebush2.html

www.agry.purdue.edu/turf/ tips/2002/clover611.htm

Age Structure

• The age structure of a population is usually shown graphically.

• The population is usually divided up into – Prereproductives (not mature enough to reproduce) – reproductives (capable of reproduction) – Postreproductives (too old to reproduce) • The age structure of a population dictates whether is will grow, shrink, or stay the same size.

Age Structure Diagrams

Positive Growth Zero Growth Negative Growth (ZPG) Pyramid Shape Vertical Edges Inverted Pyramid

Limits to Pop. Growth

Biotic Potential-

Ability of populations of a given species to increase in size

Abiotic Growth Factors (biotic potential)

• • •

Favorable Light conditions Favorable Temperatures Favorable Chemical environment – optimal levels of nutrients Biotic Growth Factors:

• • •

High reproductive rate Generalized niche Ability to migrate or disperse

• •

Adequate defense mechanisms against predators Ability to cope with adverse conditions – migration, resistance to

diseases, adapt to evtl. changes, etc.

Biotic Potential continued…

•

Intrinsic rate of increase (r)

– rate at which a pop. could grow if it had

UNLIMITED

resources.

• Not realistic! • No pop. can grow indefinitely due to factors that will slow growth eventually.

Limits to Pop. Growth continued…

•

Environmental Resistance all the factors that can limit the growth and size of pops. Abiotic Decreasing Factors:

• • •

Unfavorable light conditions – too little or too much Unfavorable Temperatures Unfavorable chemical environment - nutrients Biotic Decreasing Factors:

• • •

Low reproductive rate Specialized niche Inability to migrate or disperse

• • •

Too many competitiors Inadequate defense mechanisms Inability to cope with adverse conditions- not resistance to disease or unable to adapt to envtl. changes

Environmental Resistance continued…

•

• There is a dynamic balance between biotic potential and environmental resistance.

Carrying capacity (K)

- maximum number of individuals a habitat can support over a given period of time due to environmental resistance

(sustainability)

Population Change and Carrying Capacity

Basic Concept : Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium

(balance between births and deaths)

Measuring Pop. Growth

•

Population growth depends upon

–

birth rates

– –

death rates immigration rates (into area)

–

emigration rates (exit area)

Pop. change = (b + i) - (d + e)

Population Growth Diagrams

• Populations show two types of growth

Exponential

• J-shaped curve • Growth is independent of population density

Logistic

• S-shaped curve • Growth is not independent of population density

Exponential growth (J curve)

Fixed rate of increase, starting slowly and growing rapidly Exponential curve is

not realistic

for long periods of time, due to carrying capacity of area.

Logistic Growth (S curve)

• • • • Because of environmental resistance, population growth decreases as density reaches carrying capacity Graph of individuals vs. time yields a sigmoid or S curved growth curve Reproductive time lag causes population overshoot Population will not be steady curve due to resources (prey) and predators

Density-Dependent Controls

•

Competition for resources

•

Predation

•

Parasitism

•

Disease

Density-Independent Controls

•

Natural disasters

•

Severe weather

•

Pollution

•

Pesticide spraying

9-2: Reproductive Patterns and Survival

• Goal of every species is to produce as many offspring as possible!

• Each individual has a limited amount of energy to put towards life and reproduction • This leads to a trade-off of long life or high reproductive rate • Natural Selection has lead to two strategies for species:

r - strategists

and

K - strategists

r - Strategists

• Spend most of their time in exponential growth K • Maximize reproductive life • Minimum life

r - Strategists

• • • • • • • • • • •

Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate – (r) Population size fluctuates wildly above and below carrying capacity – (K) Generalist niche Low ability to compete Early successional species

K - Strategists • Maintain population at carrying capacity (K)

K

• Maximize lifespan

• • • • • • • • • • •

K- Strategist

Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species r and K strategists summary animation

Survivorship Curves

• • •

Late Loss (Type I) :

K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality

Constant Loss (Type II):

typically intermediate reproductive strategies with fairly constant mortality throughout all age classes

Early Loss (Type III) :

r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age

Constant Loss Early Loss Late Loss Population Growth Self Quiz!

9-3: Effects of Genetic Variations in Pop. Size Variations in genetic diversity can affect small, isolated populations. Most large pops. genetic diversity remains fairly constant.

Genetic variations that can affect small populations could include: 1. Founder effect –

few individ. colonize a new area that’s geographically isolated from others in the population

2. Demographic Bottleneck effect –

When a pop. is destroyed by natural disaster, and only a few individs. Survive; May lack genetic diversity to carry on and rebuild population.

3. Genetic drift –

random changes in genes frequencies that could lead to unequal reproductive success; founder effect could cause genetic drift

4. Inbreeding –

when individuals of small pops. mate and could increase likelihood of passing on defective genes to offspring and affect long term survival.

Genetic Drift Genetic changes in a pop. due to the Bottleneck effect

9-4: Human Impacts and Working with Nature

5.

6.

7.

8.

1.

Nine major ways humans impact the environment to meet OUR needs and wants:

Fragmentation, degrading and destroying habitats 2.

Simplifying/ homogenizing natural ecosystems

(1 crop)

3.

4.

9.

Using, wasting and destroying NPP that support all consumers.

Strengthening some populations of pest species and disease causing bacteria by overuse of pesticides Elimination of some predators

(sharks)

Deliberately or accidentally introducing new species

(exotic)

Overharvesting potentially renewable resources

(farmland, fish)

Interfering with the normal chemical cycling and energy flows in ecosystem

(excessive CO2 emissions)

Increasingly more dependent on nonrenewable energy

fuels) (fossil

Working with Nature: Principles of Sustainability

• To maintain a balance between our altered environments and natural environments, we need to learn the important features of nature.

Nature sustains itself through:

(diagram on back cover of book!)

– – – –

Uses of unlimited solar energy Biodiversity Nutrient recycling Population Control

Ecological Principles for Sustainability

(Message of the book and this class ! )

1. We are part of, not apart from, the earth’s dynamic web of life.

2. Our lives, lifestyles, and economies are totally dependent on the sun and the earth.

3. We can never do merely one thing

(first law of human ecology – Garret Hardin

).

4. Everything is connected to everything else; we are all in it together.